Built new system with the below setup in a 2 year old Antech Ninehundred case and PSU which had been working fine until the mobo, P7P55D-E Pro failed and was returned for RMA. Yesterday I got a new mobo, Saberttoth Z77, and installed all the hardware though on first boot, nothing seems to start yet the mobo has the LEDs lit. I unplugged the PSU and discovered white noise, (faint highpitched tone) came from the top of the case, close to the powerSwitch, which continues without any source of power to the case at all. The case haven't been modified in any way and have been off since the P7P55D-E Pro was pulled out.
It may not be related to the Antec Nine Hundred case but possibly other computer components such as the Power Supply. It would help if you can listen to where the sound is and then figure which one is causing the issue. If it's possibly the Nine Hundred case fan causing the noise we might be able to assist you in a getting a replacement. Please visit http://www.antec.com/support/ and fill in a trouble ticket.